Filed under: Bars / Fruit Based Bars
May 3, 2024

Oatmeal Rhubarb Bars

Crisp oatmeal bars with a layer of homemade berry rhubarb jam in the middle.

5 from 2 votes
Yield: 16 squares
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Think of an oatmeal cookie, but make it a bar, and then in that bar let’s layer in a bright, tart (ruby red!) homemade jam made with fresh raspberries and… mostly, rhubarb! 

And yes, this may be me just trying to once again use rhubarb in a cookie bar form, like I did in these blueberry rhubarb shortbread bars, but try one and blame me if you can. Rhubarb has such great flavor but I just hate the stringy texture, so I’m always looking for ways to extract that taste and usually that means making rhubarb jam. 

Recipe Origins 

This recipe is inspired and adapted from an old recipe I used to bake in college, raspberry oatmeal squares from Joy of Baking. I distinctly remember a friend of mine eating one while we were studying in the library and giving me a, wow – ‘you can bake’ nod. That said, I did not know the first thing about making homemade jam back then so I used to follow it to a T and make it with store bought jam. 

For these oatmeal rhubarb bars, I developed a homemade jam recipe with fresh rhubarb and raspberries (you can also use strawberries or blueberries). And because I’m super picky about texture, I puree and strain the jam so you just get the delicious flavors. The ‘cookie’ or bar part stayed the same but, I’ll ask you to toast the oats first so they aren’t overly soft in the bar and to use some cinnamon to enhance the flavor. 

Recipe Ingredients 

Rhubarb: fresh rhubarb, poisonous leaves removed. 

Raspberries: you can also use strawberries or blueberries. 

Starch: Tapioca or cornstarch. This is our thickening agent. 

Sugar: fine granulated sugar. 

Butter: unsalted, and softened so it can be creamed. 

Flour: all purpose flour. I haven’t tried this with oat flour (to make it gluten free) but if I were to, I’d add another ⅓ cup oat flour and let the dough rest for a bit before making the bars. A one to one gluten free flour should work too. 

Egg: one large egg. 

Cinnamon: ground cinnamon, for flavor. 

Oats: old fashioned rolled oats, not quick cooking. 

How to make Oatmeal Rhubarb Bars 

Prep the jam ingredients: slice the rhubarb into one inch slices. Toss in a pot with the raspberries, starch and sugar. 


Make the jam: set the pot over medium heat and cook until all the fruit has broken up and around it is a thick liquid, for 20-25 minutes. 

Puree & strain the jam: 

Pour the jam through a fine mesh sieve and press it as well as you can to extract as much liquid as possible (this will take some muscle and time).

*This step isn’t necessary if you like raspberry seeds and stringy bits of rhubarb.

Toast the oats: Set the oats over medium heat in a large frying pan and cook until fragrant, stirring frequently. This freshens up the oats and gives the bars a bit more texture.

Preheat the oven & prep the pan: Grease an 8×8 or a 9×9 square pan and lay two sheets of parchment paper over each other to cover all sides of the pan.

Partially melt the butter then whisk or beat the butter, sugar, cinnamon and salt until light 

Beat in the egg until creamy. 

Stir in the flour and (most of) the oats: 

Press two thirds of the mixture into the bottom of the prepared pan: 

Spread the jam: 

Add the remaining oats to the last third of the dough and crumble over the jam: 

Bake until golden all over, let cool then slice. 

How to store the Oatmeal Rhubarb Bars 

If you store them in an airtight container at room temperature, the oatmeal cookie portion will lose its crisp and become quite soft. In the fridge they’ll keep fresher longer (3-4 days). For longer storage I’d freeze them in an airtight container and let them thaw before eating.


Recipe for Oatmeal Rhubarb Bars

Oatmeal Rhubarb Bars

Crisp oatmeal bars with a layer of homemade berry rhubarb jam in the middle.
Prep Time: 30 minutes
Cook Time: 40 minutes
Yields: 16 squares
5 from 2 votes


Raspberry Rhubarb Jam

  • 150g rhubarb
  • 150g fresh raspberries or more rhubarb
  • 100g fine granulated sugar
  • 1 ½ tablespoon tapioca or cornstarch

Oat Cookie Base

  • 113g or ½ cup butter unsalted
  • 200g or 1 cup brown sugar light or dark
  • ½ tsp baking soda
  • ½ tsp fine sea salt
  • ½ tsp ground cinnamon
  • 165g or 1 ¼ cups all purpose flour
  • 1 large egg
  • 230g or 2 cups oats divided into 200g or 1 ¾ cups and 30g or ¼ cup


Make the jam

  • Set the rhubarb, raspberries, sugar and starch in a medium sized pot. Stir then set the pot over medium low heat.
  • ​​Cook for about 20-30 minutes as the raspberries burst and the rhubarb softens. Stir often and use the back of a wooden spoon to press down the rhubarb. It’s done when the consistency is thick like jam and the fruits are mushed. Set aside to cool. This can be made a few days ahead of time.

Make the oatmeal base

  • Set the oats in a large frying pan and cook over medium low heat, stirring until fragrant - about 5 minutes.
  • Preheat the oven to 350 F. Line a greased 9x9 inch square pan with parchment paper (use metal clips to hold it into place).
  • In a bowl, partially melt the butter then whisk it with the sugar, salt, soda, cinnamon and butter until creamed, about 2-4 minutes. Add the egg and beat or whisk for another minute. Add the flour and the 1 ¾ cups oats.
  • Press two thirds of the dough into the bottom of the prepared pan. Over it, spread the cooled jam.
  • Add the remaining ¼ cup oats to the oat dough, mix then use your fingers to crumble the mixture over the jam.
  • Bake the bars until golden all over, for 25-30 minutes. Let them cool in the pan then use the parchment as a sling to lift them out. Slice once they are completely cool.


Note: Recipe adapted from Joy of Baking

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Recipe Reviews

  1. 5 stars
    Made these bars last weekend after I got a bunch of rhubarb. I used strawberries instead of raspberries & didn’t strain it. I just used an immersion blender to break it down. I loved the flavor. The oatmeal base had the right amount of salt to balance the sweetness of the jam. I thought this oatmeal bar would be great with chocolate. So I might make them again & dip the bottom in chocolate or drizzle chocolate on top. Thanks for another great recipe, Sam!

  2. 5 stars
    These were delightful! I’ve never toasted oats like this before, and I love how it deepened the flavor of the oats and helped the bars become so much crispier and chewier than the typical soft oat bars. They kept well in the frig but devoured quickly! I might increase the fruit filling next time; can’t get enough rhubarb!

  3. How much jam does this make. I have homemade strawberry rhubarb jam I’d like to use up. And do you think I could sub in oat flour for the all pourpose? Want to make gluten free.